The invention relates to the field of brakes and in particular of motor vehicle brakes. To be more precise, the invention relates to a brake actuator which can be actuated by an electric motor.
Brake actuators which can be actuated by an electric motor are used both for service brakes and for hand brakes (also called parking brakes) of motor vehicles. The advantage of this design with respect to brakes which are actuated solely by means of cables or hydraulics is the fact that the driver does not have to apply a high muscular force in order to actuate the brake. An electrically actuated brake can also be effectively combined with modern vehicle electronics. Both the application and the release of the brake can therefore be made dependent on other recorded events or measured values. For example, the brake can be released in an automated manner for a “hill start”, so that the driver does not have to operate the brake in addition to the interplay of the accelerator and the clutch. If the vehicle has an automatic gearbox, actuation of the accelerator pedal can suffice to start on a hill without causing the vehicle to roll in the wrong direction and without operating the drive motor at an unfavourable operating point.
Several of the known proposals integrate the brake actuator with the caliper and the friction linings directly at the vehicle wheel. If appropriately designed, vehicle brakes equipped in this way can form, for example, autonomous systems which are also reliable in operation without communication with a central control unit.
In order to attain the power required for brake actuation in electrically operated brake actuators, the torque of an electric motor is as a rule reduced via one or a plurality of gear stage(s). The respective gear stage types can in this case vary, with spur, worm, planetary, rolling body or belt gear mechanisms being usual. The latter have proved to be particularly successful in motor vehicle construction, as, in contrast to most other types of gear, they have good noise-damping properties and are therefore capable of effectively isolating the structure-borne noise produced by the electric motor from the rest of the drive train.
It has become apparent that, in spite of the good noise-damping properties of belt gear mechanisms, the expected noise damping of the entire brake actuator is often not achieved, as in some cases other components of the actuator transmit the vibrations produced by the electric motor around the belt unit. Solutions which permit complete isolation of the structure-borne noise caused by the electric motor from a subsequent drive train are expensive to manufacture and assemble, are often susceptible to faults on account of the high number of parts used and, moreover, may impair the precision in the torque transmission of the entire gear assembly.